diff --git a/scrapling/spiders/checkpoint.py b/scrapling/spiders/checkpoint.py
index 4c511ae..aa84432 100644
--- a/scrapling/spiders/checkpoint.py
+++ b/scrapling/spiders/checkpoint.py
@@ -32,7 +32,7 @@ class CheckpointManager:
         if not isinstance(interval, (int, float)):
             raise TypeError("Checkpoints interval must be integer or float.")
         else:
-            if interval < 0:
+            if interval <= 0:
                 raise ValueError("Checkpoints interval must be greater than 0.")
 
     async def has_checkpoint(self) -> bool:
diff --git a/scrapling/spiders/request.py b/scrapling/spiders/request.py
index edfc387..ce728ee 100644
--- a/scrapling/spiders/request.py
+++ b/scrapling/spiders/request.py
@@ -85,8 +85,6 @@ class Request:
                 body = post_data.getvalue()
             elif isinstance(post_data, bytes):
                 body = post_data
-            elif post_data is None:
-                body = b""
         else:
             post_data = self._session_kwargs.get("json", {})
             body = orjson.dumps(post_data) if post_data else b""
diff --git a/scrapling/spiders/result.py b/scrapling/spiders/result.py
index eeb5522..08a7658 100644
--- a/scrapling/spiders/result.py
+++ b/scrapling/spiders/result.py
@@ -15,7 +15,6 @@ class ItemList(list):
 
         :param path: Path to the output file
         :param indent: Pretty-print with 2-space indentation (slightly slower)
-        :return: Number of items written
         """
         options = orjson.OPT_SERIALIZE_NUMPY
         if indent:
diff --git a/scrapling/spiders/spider.py b/scrapling/spiders/spider.py
index c994d2b..4f38912 100644
--- a/scrapling/spiders/spider.py
+++ b/scrapling/spiders/spider.py
@@ -79,9 +79,9 @@ class Spider(ABC):
     max_blocked_retries: int = 3
 
     # Fingerprint adjustments
-    fp_include_kwargs = False
-    fp_keep_fragments = False
-    fp_include_headers = False
+    fp_include_kwargs: bool = False
+    fp_keep_fragments: bool = False
+    fp_include_headers: bool = False
 
     # Logging settings
     logging_level: int = logging.DEBUG